1. Field of the Invention
This invention relates to an apparatus on which an endless belt/belt sleeve is mounted for rotational movement in an endless path around spaced rollers to allow a cutting/grinding operation to be performed thereon and, more particularly, to an apparatus which limits deviation of the endless belt/belt sleeve from a desired rotational path. This invention further relates to a grinding wheel for treating a surface of a power transmission belt/belt sleeve as, for example, the back surface of an endless belt/belt sleeve trained to rotate stably around spaced rollers and, more particularly, to a grinding wheel which effects precise treatment of a power transmission belt while minimizing heat generation. This invention is still further directed to a method of using the belt processing apparatus, including a grinding wheel that is a part thereof.
2. Background Art
It is known to fabricate power transmission belts, such as multi-ribbed belts, by sequentially building components inside out on a forming drum/mandrel. More particularly, a canvas layer, outer tension rubber layer, load carrying section and inside compression rubber layer are placed in turn on the forming drum to define a belt sleeve which is thereafter vulcanized. It is also known to rotate an endless sleeve formed by this method on a forming drum and to define V-shaped grooves in the rotating belt sleeve by means of a grinder having a cylindrical cutting surface that is complementary to the desired groove configuration in the belt sleeve. An exemplary system of this type is shown in Japanese Patent Publication No. 52-17552.
Multi-ribbed belts are commonly used in drive systems such as serpentine drive systems in automobiles. Typically, one very long belt drives numerous belt components. Since it would be impractical to use a forming drum to support such a belt/belt sleeve, in that the radius would be unduly large, such belts are commonly formed by training a belt/belt sleeve around spaced rollers having parallel axes. One or both of the rollers are driven to effect rotation of the belt/belt sleeve. The belt grooves are formed in the belt/belt sleeve using a grinding wheel similar to that used in forming side edges and grooves in a belt/belt sleeve carried by a forming drum. One of the rollers serves as a backing surface for the grinding wheel.
The above two forming methods are utilized not only on multi-ribbed belts but also to define the side surfaces of a conventional V-belt and to separate the individual belts from the belt sleeve using a cutter blade.
The above two techniques are further utilized to grind the back surface of the belt sleeve to produce a uniform thickness for the belt sleeve and the belts ultimately separated therefrom.
Particularly in the latter technique, in order to uniformly produce high quality belts, it is important to limit the deviation of the endless belt/belt sleeve from a predetermined rotational path around the two rollers. This objective is commonly frustrated by the load-carrying cords defining the neutral belt axis. Typically, a plurality of laterally spaced load-carrying cords are embedded in a rubber layer. The individual cords are conventionally made from twisted fibers and naturally bias the belt in a direction that depends on the direction of winding i.e. whether the twisted cords are "S-type" or "Z-type". When an individual belt/belt sleeve is trained around spaced rollers, there is a tendency of the belt/belt sleeve to shift laterally depending upon the twist direction. Further, any inclination of the load-carrying cords can produce the same undesirable result.
The result of the above lateral shifting is that the individual belt dimensions may vary from one belt to the next. This problem is particularly prevalent using conventional grinding techniques. By such techniques, the grinding wheel is urged against the rotating belt sleeve to cut/grind a portion thereof. Once that portion of the belt sleeve is formed, the grinding structure is retracted and shifted laterally to progressively form the belt sleeve. As long as the grinding wheel or cutter is pressed against the belt sleeve, the lateral shifting is minimized. However, once the cutting/grinding element is retracted fully from the belt sleeve, there is a tendency of the freely rotating belt sleeve to shift laterally as a result of the bias from the load-carrying cords. Further, the cut/ground portion of the belt sleeve becomes more flexible than the remainder of the belt sleeve which may lead to shifting of the belt sleeve. The result of this is that the width of the belts and/or ribs cut/ground out of the belt sleeve may be irregular.
One proposed solution to the above problem has been to alternatingly wrap "S-type" and "Z-type" load-carrying cords during formation of the belt sleeve. While alternating cords can alleviate the shifting problem to a certain extent, it does not provide a solution in a belt sleeve wherein a cord is continuously wound. The cords are slightly inclined to produce a spiral arrangement which results in a lateral bias on the belt sleeve. In this case, the alternating arrangement of "Z-type" and "S-type" cords does not provide an adequate solution to belt deviation during belt rotation.
As an alternative solution, it is known to provide a raised crown on at least one of the rollers in the spaced roller pair. The crown surface tends to block lateral shifting of the belt/belt sleeve. However, there is also a tendency of the belt/belt sleeve to bend radially outwardly to conform to the crown surface. The result is deformation of the belt sleeve and the individual belts formed from that part of the belt sleeve adjacent to the laterally opposite edges thereof.
Accurate grinding of a power transmission belt/belt sleeve is also compromised due to the nature of the conventional grinding wheel. Typically, a grinding wheel body has ribs, which are triangularly-shaped in cross section, projecting radially outwardly therefrom, with there being grooves alternating with the ribs along the axial extent of the grinding wheel. The ribs and grooves extend uninterruptedly around the circumference of the body. The cross sections of the ribs and adjacent grooves are chosen to be complementary to the end configuration for the belt sleeve. Diamond particles, or other hard granular material, can be placed on the cutting surface to improve the cutting capabilities for the grinding wheel.
One particular problem with the conventional grinding wheel is that the rotating grinding wheel remains continuously in contact with the belt during treatment. Through friction, both the grinding wheel and belt become heated. This causes a situation referred to in the art as belt reversion. The heated belt expands and is ground in its expanded state. Once the treated belt contracts, the contour thereof varies. The result is that belts treated using conventional grinding wheels are inconsistently shaped, from one to the next.
A further problem with belt manufacture utilizing the conventional grinding wheel is that the heat generation and resulting expansion of the belt/belt sleeve cause binding between the belt/belt sleeve and grinding wheel. This necessitates greater power consumption to rotate the grinding wheel at the desired angular velocity. Alternatively, the grinding wheel is operated at a slower speed, in which event the grinding operation must proceed more slowly. Increased power consumption results and increases manufacturing costs.